1. Field of the Invention
The present invention relates to an image forming apparatus capable of recording images on both sides of a recording sheet or recording images in an overlaying manner on the already recorded sheet.
2. Description of the Related Art
There exist copiers capable of double-sided or overlay recording whereby images are copied onto both sides of every sheet or onto one side thereof with images already recorded thereon. This type of double-sided or overlay recording copiers works essentially as follows: a first original document is copied initially onto the predetermined number of recording sheets. All copied sheets are stored temporarily in an intermediate tray. Then a second original document is copied onto the initially copied sheets that are refed from the intermediate tray.
It can be seen that the conventional process of double-side or overlay recording allows copying of the second original document to proceed only after all the initially copied sheets derived from the first document have been stored in the intermediate tray. The waiting period interposed between the two distinct stages of copying inevitably lowers productivity of double-sided or overlay recording, i.e., reduces the number of sheets that may be copied per unit time.
One solution to the above problem is for the double-sided or overlay copying machine to start copying the second document onto the initially copied sheets before these sheets are all placed into the intermediate tray. That is, after the first original document has been scanned for the predetermined number of copying sheets, these sheets should preferably be subjected to copying of the second document before all of them are stored into the intermediate tray. Productivity should be increased if the waiting period following the copying of the first original document were eliminated.
Conventionally, the above solution has been ignored primarily for the following reason: in the putative setup of the solution, even as the initially copied recording sheets are being stored into the intermediate tray, those sheets already placed in that tray should be refed therefrom to the second stage of copying. The incoming and the outgoing sheets within the intermediate tray would interfere with one another, resulting in an incidental dragged-along feed or jamming of sheets.